It's basic human psychology. People who lack the ability to think for themselves are easily suckered into identifying themselves with groups, identifying themselves in such a way that they BECOME the group. As such, they will react violently towards anything that threatens their group...

Or that they feel may threaten their group, even when in fact it doesn't. This is something that you can also see in open source projects, where for many loyalty to the group becomes more important than objectivity. Great observation Thom!